<?php
class Dvd extends Product
{
	private $time;
	
	public function __toString(){
		echo $this->time;
	}
	
	public function __get($name){
		return $this->name;
	}
	
	public function __set($name, $value){
		$this->time = $value;
	}
}

$liuhuan = new Dvd();
$liuhuan->time;
$liuhuan->height = 178;